Rovers however fought back after the break and grabbed a deserved equaliser when Brett Emerton scored on 64 minutes to leave the Baggies in the bottom three in the table with three games to play.
"It’s disappointing because we got in front, but in our situation you need the second," Robson said after the 1-1 draw.
"We had a few opportunities that could have killed the game.
"We played well at the start of the second half and Neil Clement had a great chance with a header.
"We also had a few decent penalty shouts and the one with Kevin Campbell was a blatant penalty."